This invention is related to the field of earth boring tools, and in particular to a method and apparatus for directing drilling fluid to the cutting edges of various downhole drilling bit cutters, most likely polycrystalline diamond cutters (PDCs). More particularly, this invention discloses the invention of a channeling system in the upper part of a cutter's front surface which focuses the drilling fluid flow right at the cutting tip of the cutter, thereby maximizing the cleaning and cooling effect of the fluid flow on the actual cutting surface.
In the past, drilling fluid has generally been introduced to the face of a bit through passageways or nozzles in a bit. The drilling fluid would flow around the bit, more particularly the cutting face of the bit, thereby cooling the bit and washing the cutting elements so that they would present a clean cutting face. The drilling fluid would then move the cuttings to the gauge of the bit and there lift them up the annulus between the drill string and the wall of the bore hole.
For example, U.S. Pat. No. 4,098,363 discloses a design of a bit where the nozzles are positioned in the junk slots in the face of the bit with their axes oriented and so distributed across the face of the bit that the ejected streams of drilling fluid wash over the cutters and cover substantially the entire surface of the formation being cut by the bit when the bit is rotated. The longitudinal arrays of cutters therein are separated by the junk slots which also serve as water courses. The arrays of nozzles within the drill bit fluid channels produce a fluid flow of such velocity that bit cleaning and detritus removal is facilitated.
In order to improve the cleaning and detritus removal action of the drilling fluid flow from such nozzles, specific nozzle arrays and directions have been proposed and used in the design of drilling bits. For example, as disclosed in U.S. Pat. No. 4,471,845, the outlet cones of nozzles have been so dimensioned that all the cutting elements on a drill bit have been supplied with flushing fluid flow. Furthermore, the alignment of the nozzles has been varied depending on which direction of the flushing stream is desired with regard to optimum cutting bit cooling and cutting removal action. As further disclosed in U.S. Pat. No. 4,471,845, certain nozzles have been aligned so that they impress a direction tangential to the drill bit towards the cutting elements on the flushing stream, whereas other nozzles have been aligned to impress a radial component towards the marginal region of the bit on the flushing stream.
The fluid nozzles in a drill bit, as shown in U.S. Pat. No. 4,452,324, have also been variously curved and thereby their flow directed towards the cutting members. This alignment gives the jets of the flushing fluid emerging from the curved nozzles an alignment with at least one component facing in the direction of the drillings flowing off along the outer face of the body.
Furthermore, bits have also been designed with a multiplicity of individual diamond insert studs which include an axially aligned fluid passage formed within the insert stud which communicates with a fluid-filled chamber formed by the drag bit. The fluid exits the passage in the stud in front of the diamond cutting face of the stud to assure cooling and cleaning of each insert stud inserted in the face of the drag bit. One such design is disclosed in U.S. Pat. No. 4,303,136.
In one development, as disclosed in U.S. Pat. No. 4,606,418, the discharge nozzle is actually placed within the cutting face itself and directs drilling fluid away from the cutting face and into the formation to be cut. There are, however, associated problems with this development such as the clogging of the nozzle by the formation and ineffective cooling of the cutter cutting tip.
In another development, as disclosed in U.S. Pat. No. 4,852,671, the cutting disc edge and the leading end of the stud the disc is mounted on include a channel meant to conduct cooling fluid to the cutting points to clean and cool the same. These two cutting edge segments, however, wear at a faster rate than the usual single cutting edge and the channel could clog and thereby become ineffective for conducting cooling fluid.
In some recent improvements, such as that disclosed in U.S. Pat. No. 4,883,132, hydraulic nozzles are defined in the bit body beneath and azimuthally behind the arches formed by each blade. The nozzles direct hydraulic flow across the cavity under the arch and across each portion of the cutting face on the arch. As a result, when cutting, substantially only a diamond surface is provided for shearing a rock formation or contacting with velocity any portion of the plastic rock formation. Once the rock chip is extruded upwardly across the diamond face of the cutter, it is subjected to a directed hydraulic flow which peels the chip from the diamond face and transports it into the open cavity designed underneath the arch blade.
In an even more recent improvement, as disclosed in U.S. Pat. No. 4,913,244, an improved rotating drag bit for cutting plastic, sticky, water reactive, and shell formations is devised wherein each large cutter is provided with at least one hydraulic nozzle which in turn provides a directed hydraulic flow at the corresponding cutter face. The directed hydraulic flow is positioned to apply a force to the chip which tends to peel the chip away from the cutter face. In addition, the hydraulic flow is positioned with respect to the chip so as to apply an off-center torque to the chip which is used to peel the chip away from the cutter face and toward the gauge of the bit.
As one can see from the above description of the prior art, in most current dedicated hydraulic bit designs, a fluid stream is directed at the flat face of a cutter. Upon hitting this face, the fluid flow spreads out over the surface. The spreading out of the flow is not controlled in any way and, therefore, certain portions of the cutting face of the cutter may get more or less flow depending on the nozzle direction and conditions down hole. However, it is the actual cutting tip of the cutter which needs the maximum cooling and cleaning action of the fluid flow in order for the drill bit as a whole to function most efficiently and economically.